text:
After the most recent US instructions, are there any prohibitions against transporting spare lithium ion/metal batteries in the cabin?
Per the recent directive from Transportation Security Administration (TSA), except for medical devices, electronic devices which are larger than a cell phone/smart phone cannot be carried in the cabin of the aircraft from some countries into the United States. Many airlines are implementing this instruction and are requesting that all passengers traveling to the United States pack all electronic devices larger than a smart phone in their checked-in baggage.
The ICAO, IATA & FAA have already prohibited carrying spare lithium ion and/or lithium metal batteries in the aircraft hold area.
Is the transportation of spare lithium ion and/or lithium metal batteries in the passenger cabin of the aircraft now prohibited? Is it considered a rule violation to carry spare batteries this way?
Where can the spare lithium ion and/or lithium metal batteries be stowed during the prohibition period and how can they be transported?

If the risk is so high, how airline companies can allow the electronic devices operated by lithium ion battery such as laptops, cameras, tablets packed in a checked baggage be loaded in a belly compartment of an aircraft. How to make sure that all electronic devices operated by lithium ion battery stowed in a checked baggage protected.

@mins, quite a few incidents were reported already where a lithium-battery-powered device has ignited on board of an aircraft. In the cabin, the established procedure is to dump the device in a bucket of water, which will safely contain the thermal runaway. However, there is no access to the cargo bay in flight in most aircraft, so it can't be used there. The extinguisher should be able to prevent the fire spreading much, but it would still probably do significant damage.

Short answer: Yes.
Slightly longer answer: IATA changed the regulations within the 58th Edition of the Dangerous Goods Guidelines, effective January 1st, 2017. For passenger aircraft, lithium batteries are only allowed if they are installed in equipment. Standalone lithium ion cells or batteries are no longer permitted on passenger aircraft.
If you want to air freight lithium batteries: Air transport of Lithium batteries is only allowed if they are charged to 30% or less of their nominal capacity. Also, the cell must comply with the United Nations (UN) Manual of Tests and Criteria, Part III, Sub‐Section 38.3 (see page 394ff in this document) and proper packaging and documentation must be ensured.
The rules in the US and elsewhere differ slightly. From this Energizer document on US air freight:

Batteries must be of a type proven to meet the requirements of each test in the UN Manual of Tests and Criteria.

Batteries must be packed in strong outer packaging and be packaged in a manner to prevent short circuits and separated so that electrically active terminals cannot come into contact with each other.

The gross weight of the shippable container shall not exceed 30 kg. 

For lithium‐ion cell, the equivalent lithium content is not more than 1.5 g; or lithium‐ion battery, the aggregate equivalent lithium content is not more than 8 g.

The shippable container must be capable of passing a 1.2 m. drop test in any orientation without spillage of the contents of the packaging, damage to the batteries inside or shifting of the contents that could lead to short circuit.

The shippable container must be marked to indicate lithium batteries are present and that special procedures should be followed if the package is damaged.

So, I can't take a second battery for my camera with me... Nice... However, is a power bank a battery, or a device in this context?

@sweber: That depends on the discretion of the airline staff. The 30% charge limit can be exceeded, for example, if the authorities in both the origin and destination country allow. When I purchase Li-ion-cells from China, they are routinely charged to 70% or more. Similar leeway exists in interpretation what exactly is equipment.

Dear Peter, thank u for your answer. When i check iata website it shows that spare lithium ion batteries with watt-hour rating equal/less than 100Wh can be carried in the passenger cabin without limit and maximum 2 pcs of lithium ion batteries with watt-hour rating greater than 100Wh but equal/less than 160Wh can be carried in the passenger cabin Can you tell me the exact reference chapter regarding standalone lithium batteries are no longer permitted to the aircraft.

@GolfCharlie: I admit that I did not dig as deeply as you. My reference is this overview page. The linked document only contains the changes - the "real" IATA rules are more extensive. As I understand it, the size limits apply to airfreight, not passenger aircraft.


text:
Why does the headset man not get on the tractor?
As far as I can see, the pushback operation of a passenger aircraft is carried out by a similar application at many airports. It's a towbarless tractor and driver who pushes the aircraft together with a headset man connected to the aircraft walking next to the tractor.
It's strange for me to walk for minutes instead of getting on the tractor. The task of the headset man getting on a tractor will make both time efficient and less tiring. And it’ll be more faster than conventional push-out as well. Isn’t it?

(Source: wikimedia.org)

The "headset man" is a wing walker, and he is there for a reason - he is not just someone who needs a ride to where the aircraft is being pushed to. Essentially, he is an extra pair of eyes for the tow driver. He needs be able to see everything going on around the aircraft to avoid collisions with other aircraft or stationary objects. This task cannot be performed from within the tow truck since the view from there is relatively limited.

Actually i didn’t mean headset man to take a seat next to driver. I think the headset man be able to see everything around aircraft while standing on the side platform of the tractor(outside of the tractor, standing and facing towards the aircraft) Would not it be safer to stand on tractor’s side platform than walking on the ground? In my opinion it’s more dangerous to walk alongside the tractor.

@GolfCharlie no that would be a lot more dangerous. A fall from that height (which will happen occasionally) can be lethal if the head hits the floor. Regardless, the pushback would be at the same speed even without the wing walker.

If he needs to be out there to have a good view of the wing tip, is his walking speed limiting the tractor? Is there some other factor limiting speed, or are the distances so short that it's not worth providing him with a vehicle (even a bicycle)?

If you're pushing a jetliner back at a pace faster than walking speed, you need to ask what's the hurry.

@RobCrawford The pushback operation at walking speed can last over 5 minutes. When hundreds of pushbacks are done a day, I think the time spent on pushback operation can find hours. I just wanted to know how to shorten this process without compromising safety of the ground crew/aircraft and how to get past long distance walking of headset man.

@GolfCharlie It's important for the operation to be slow for a number of reasons. First of all, it makes it much easier to stop quickly if a wingtip gets too close to something or if something unexpectedly moves into the aircraft's pushback path. The extra maybe 20-30 seconds aren't worth the potential of doing millions upon millions of dollars of damage to the aircraft (or people!) Second, the way tricycle gear aircraft are designed, if they're moving backwards quickly and stop suddenly, they could potentially tip backwards onto their tail due to their momentum. That's no good.

Actually the "headset man" is the line maintenance a.k.a. mechanic.
The headset is plugged into the airplane and is in direct communication with the cockpit. It's more precisely known as a "telephone".
Callsigns are usually "cockpit" for cockpit and "ground" for the mechanic.
"Ground" informs the "cockpit" when to release the parking brakes (when it is connected to the paymover and chocks are off).
Cockpit tells "ground" when done and in which direction to pushback the plane.
He walks beside the airplane so he has a better and less obstructed view of the airplane surroundings, he clears the crew for the engine start up checking that the engines are clear and monitors it.
He also supervises the tow bar disconnection and removes the nose gear pin. He checks everything is clear (trucks, people, etc.) and clears the plane to taxi after showing the crew the pin so that they can visually confirm it has been removed.

I don't think they are maintenance personnel or mechanics.

Costs, effectivity, and safety are the main concerns.
If that person now has to drive a tractor around the tarmac, the airport would have to pay for tens and hundreds of tractors and their maintenance costs (such as fuel etc).
The person driving the tractor also has to focus on the road, and you can't move around as you wish with a tractor on an airport to observe.
If you are elevated on a tractor, you may not be able to observe what's going on under the aircraft. Is there a fire? A spark or two? We may never now.
Safety concerns are a thing too; how close can the tractor come to the aircraft? What happens if they colllide? That's extra costs for the airport. The person in the tractor has to be connected to the aircraft via a wire so range is a question here.
Airport vehicles have to have a beacon light during movement. This is to alert vehicles around (including planes) that they are moving and could be a risk. If a plane pushes back during night, a light of another vehicle could be mistaken for the truck which elevates the risks of an accident happening.
Those are the debatable reasons I could think of.

I think OP is asking why the person doesn't ride along on the tow truck, not why he doesn't have a separate tractor. Your points are still valid, though.

@J.Hougaard Ah gotcha, I read OPs comment on the first answer a little too fast hehe

The problem with riding on the tractor is that the observer ends up with nearly the same visual perspective as the tractor operator. While it may be possible that a  tractor-riding "wing walker" could have fewer visual obstructions than the person behind the wheel, the "walker" would still only be a few feet away from the driver, and see nearly the same view as the driver. When you're pushing aircraft with wingspans between 100 to 200 feet, you really need someone "out there" to make sure the wingtips are not going to clip something.

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text:
What is the difference between the words "airlines" and "airways" semantically?
I wonder what the difference between the words "airlines" and "airways" is. Do you have any information on this?
I am asking this question to find out why some air carriers use "airlines" while others use "airways" on their brand names.

Probably better asked on http://english.stackexchange.com/

It isn't completely clear to me what you're asking here, can you add some more information and even examples of phrases that you want to clarify? For example, are you simply asking what is "an airway" and what is "an airline"? Or, as mentioned in a comment, are you asking why "British Airways" but "American Airlines"? Depending on what you're really asking, as @J.Hougaard suggested you may get a better response on english.SE.

3 excellent answers depending on which question, exactly, is the intended one. Even so, probably still better on [English.SE], or, possibly [ELL.SE].

@mins - inter means internal, not external.

@davor, I'm not sure what your comment is referring to, but "inter" usually means external, and more specifically means "between" two different things or places. The opposite word is "intra", for internal to a location or thing. For example, interstate means to go from one state to another. Intrastate means to stay within a state. Some companies process data on their intranet (internal to their company), and then send that data elsewhere on the internet (which goes external from network to network)

This answer assumes that you are asking about the business name chosen by various air transport companies, such as "American Airlines" vs "British Airways".

Short answer:
There is no difference semantically. It's purely a marketing decision. The company decides which "sounds better", and uses that as their official business name. There are several other similar nouns used in business names as well:

"Air" (either before or after): Air France. Korean Air. Or even as part of the name: Ryanair.
"Aviation": Grant Aviation.
And then don't forget that Delta uses a space:  Delta Air Lines.
And then there are even some companies using several different nouns throughout their sub-divisions:  "Trans Executive Airlines of Hawaii" is the name of a single airline company, but their cargo services are performed under the name "Transair", and their passenger services are performed under the name "Interisland Airways"

Long answer:
There is some historical context, going back to the days when ocean travel was the only form of international travel between continents separated by oceans. A "line" was a route between two points. A "liner", then, was a ship that sailed that line. Since it was on the ocean, it was commonly called an Ocean Liner, and companies that popped up to provide a scheduled service on those lines used the term "line" or "liner" in their name: Black Ball Line, or American President Lines.
When Trains came into being, they took up the same vernacular from their ocean transport heritage. The system of rails between two points was usually built by a company for its own use, and was sometimes called a "railroad", or a "railway", with no discernible reason why some chose one term over the other. The term "line" was still used, interwoven into the industry: a "main line" was a company's main route between two cities, and a "spur line" would branch off to a smaller town.  Some companies named themselves with either the "roads" or the "ways" part: The Kansas Pacific Railway, or the Western Pacific Railroad.
The next major transformation in the transportation industry was air travel, which again borrowed terminology from both its ocean and rail heritage. An "air line" was a route between two points, and an aircraft providing service on that line was an "air liner", and company names went one of two directions: Air Lines (such as "Eastern Air Lines"), or Airways (such as "Western Canadian Airways")
The terms "air liner" (for an aircraft) and "air line" (for a company) eventually worked their way into the single-word terms as we know them, and they are officially defined, today.
But even in the early days, there were still many different nouns working their way into the company names: National Air Transport, Western Air Express, or Ford Air Transport Service. Following the Air Mail Scandal, (in which existing companies had to give up their air mail routes), many companies either merged or simply changed their names to re-gain air mail contracts. Several companies with names of XXX Air Lines (with the space) simply changed to XXX Airlines (without the space), and this is now why we see this term (Airlines) in company names today.  (with Delta Air Lines being a notable difference)

Ha! Thanks for the catch, and the edit, @freeman.  I'm also a proud member of the Grammar Police, and usually carry out my duties to "Serve and Correct" faithfully.  I loath seeing apostrophe catastrophes; but, even worse when I make them myself.

Apostrophe Catastrophe.  I call band name!

This would be a good question for English Language and Usage.se. The two terms are almost entirely synonymous, but come from slightly different etymologies.
Air travel borrows a lot of its language from previous forms of travel. "Way" is an old word that has developed a ton of different meanings. It originally indicated a path or route. It also indicated passage, as in right of way. When the Romans built roads it became a name for that, roadway. When trains came along it was a rail road or railway. Railroad companies are often called railways. It's used in shipping also, such as a waybill. It was simply borrowed into the aviation industry, both in the names of companies and the "roads" or routes in the sky designated for navigation.
The main source of words for aviation is ocean shipping, which itself adopted a few terms from rail travel. Before a railroad can go somewhere you must first lay down lines. The word was also used for the routes. Eventually it was used for the whole idea of a scheduled system of routes.
The idea of a scheduled system of origins and destinations was then borrowed into shipping. Passenger boats become ocean liners and the companies were often called things such as White Star Line. So it evolved from a description of actual train tracks, to a system of routing to the company itself.
When aircraft came along they borrowed a lot of terminology from shipping. This is where we get airlines. There are a ton of examples of terms borrowed from shipping. That's certainly why, since we get on boats, we also get on planes. But as George Carlin noted, I much prefer to get in the plane.

Other than the fact that boat travel came along long before rail travel, I think you're spot on.

@FreeMan Boat travel preceded railroads and rail borrowed a ton of terms from shipping, but it seems when I was looking this up once, a long time ago, many of the terms dealing with the industry (as opposed to the operation) came along during the first industrial revolution. It's been a long time since I read all that stuff, and I might be mistaken, but I believe "way" goes back to the renaissance in shipping. "Line," on the other hand, was only used in shipping for ropes and the second meaning was first used in rail. When I get some time I'll see if I can pin down some dates on it.

@FreeMan I also did a lot of cut and pasting while I was writing the answer and I notice I had a few things in one paragraph that were originally from another.

Wiki
An airline is a company that provides air transport services for traveling passengers and freight. Airlines utilize aircraft to supply these services and may form partnerships or alliances with other airlines for codeshare agreements. Generally, airline companies are recognized with an air operating certificate or license issued by a governmental aviation body.
Source
An airway is:
A control area or portion thereof established in the form of a corridor. (ICAO Annex 11 - Air traffic Services).
A control area or portion thereof established in the form of a corridor equipped with radio navigation aids. (EUROCONTROL EATM Glossary of Terms)
The lateral and vertical extent of airways is detailed in the appropriate national AIP(Aeronautical information publication).

I think intent of the question is more along the lines of: what is the difference between American Airlines, and British Airways.

Airway: The aviation equivalent of a motorway(UK)/highway(US).

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text:
Laminating required documents?
Airworthiness Certificates, Registration Certificates, Radio Licenses, Medical Certificates, Temporary Airman Certificates and other important documents are commonly printed on paper, which can be easily damaged or destroyed. Replacement can take weeks or months, grounding the plane or pilot unnecessarily.
Is there any regulation (or other general legal principle regarding official documents) that prohibits lamination to protect them?  If so, is there another widely accepted solution?

Just make copies of your documents.  You won't be grounded for eons if you have backup evidence.  Take pictures of everything with your phone and email the pics to yourself.

FYI a family member of mine had a problem getting a "Real ID" driver's license because he had laminated his Social Security card.  So the accepted answer may not apply to non-FAA-issued documents, or to cases where documents are being presented to someone other than an FAA official.

You may laminate certificates after any required signatures are made.
For pilot certificates, we find this in FAA Order 8900.1:

5-196    PERSONAL POSSESSION OF PILOT CERTIFICATES. Title 14 of the Code of Federal Regulations (14 CFR) part 61, § 61.3 ...
NOTE:  Airmen may either use clear laminating sheets to protect permanent FAA-issued certificates or have the certificates professionally laminated, as long as the airman’s signature is placed on the certificate before lamination. Without the signature, the certificate is not valid.

The FAA also allows lamination of aircraft airworthiness certificates. From FAA Order 8130.2J:

When printing a (airworthiness) certificate using the PDF version of the form, set the page scaling to none, or actual size.  The printed form should be approximately 5½”by 3-3/8”. Use white 8½” by 11” paper (if the applicant wishes, they may trim the document to size) or appropriate size card stock. You should use a heavy weight paper or cardstock. The forms will print in grayscale; using a color printer is not required. Laser print may be subject to displacement.  Encourage applicants to protect the document by lamination or other document protection processes.

For protecting non-wallet documents, consider using a vacuum seal bag for food. To prevent warping the simplest thing is to squeeze the air out and only use the seal function, without vacuum.
This way way if somebody has an issue or you need to modify the documents, you can cut open the pouch and retrieve them in original state.

similar things exist as dedicated document sleeves as well. Might be less messy if you work for a company that has such a device.

@jwenting I seem to recall seeing something like that, thermally sealed on the edges but I can't find it. You have a link?

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text:
What is the reason for the pressure drop in the combustion section of a jet engine?
In a reciprocating engine, ignition increases gas pressure. Why is this not the case in a turbine engine? This graph, from this question, shows in green the pressure in a jet engine:

The temperature increases by 1,500°C during combustion, but the pressure drops.

The pressure loss in the combustion chamber is attributed by two
causes:

Friction (with the liner), mixing and turbulence
The temperature rise due to the combustion of fuel. This pressure loss is called the “fundamental pressure loss”. An increase in temperature causes a decrease in density and therefore an increase in local velocity of the flow. Pressure losses are proportional with the square of the flow velocity.

The air moves¹ in direction of decreasing pressure except where forced by the compressor. So the pressure must be decreasing to maintain desired flow. If the pressure was increasing, the flow would stop and reverse and the engine would stop operating.
In fact, that's exactly what happens if fuel is added too fast: the energy quickly raises, but the still slow-spinning turbine provides too much resistance, so pressure will increase above what the compressor can provide and the compressor will stall, the engine will emit loud bang and some flames from both ends and likely flame out as it runs out of oxygen for a moment.
As already explained, in the normal flow the released energy increases the velocity of the flow instead of pressure.

¹ More precisely accelerates. If the pressure was constant, it would keep moving. But it must not raise. It decreases slightly due to friction.

Ideally in brayton Cycle the process is constant pressure heat addition and the fact that combustion chamber is left open allows it to expand thus pressure doesn't increase.But I have also heard that combustion chambers in gas turbine engines are designed by considering the flow as Rayleigh flow.And in a Rayleigh flow for subsonic case the static and stagnation pressure decreases during heat addition.So is the flow Rayleigh flow?

@AbhishekPallipparagopakumar: It seems, in first approximation: "The combustion chambers inside turbojet engines usually have a constant area and the fuel mass addition is negligible. These properties make the Rayleigh flow model applicable for heat addition to the flow through combustion". In annular combustor, the pressure drop is about 2%, mostly due to (cold) friction. Source (p. 66)

@mins yes you are right. I had found from another Q&A that Rayleigh flow is indeed applicable and the fact that mass addition being very small clearly supports the assumption. Although I was actually confused about the pressure drop occurring in combustion chamber being solely attributed to frictional drops or does the pressure drop during Rayleigh flow has a part in it. From the Q&A it does have a part.

@AbhishekPallipparagopakumar: That's my understanding. Same document, p.70: "The heat addition causes a decrease in stagnation pressure which is known as the Rayleigh effect and is critical in the design of combustion systems". According to Farokhi, the pressure loss range for heat release is 0.5-1%, the "friction" (cold) loss is 4-7% for some combustion chamber.

@mins I have just quickly read through a few pages of the text (the math is too complex to indulge with) and If I am right the pressure loss due to heat addition increases as the flow speed increases and the presence of a diffuser to ensure low Mach at the inlet of combustion chamber keeps the hot loses comparatively low. They have also used the Bernoulli's equation, assuming the flow to be incompressible within cc and determined the hot pressure losses.

@AbhishekPallipparagopakumar: I read that too. The first document explains how to determine "Mach number, pressure and temperature of the gas at exit and [...] the stagnation pressure loss during heating", page 76, problem 2.14. While there are equations, the reasoning is well explained and can be understood without the equations. I assume this loss is welcome to maintain the pressure inside the liners lower than in the combustor case, to allow swirling/cooling air to cross the liner holes and prevent hot gas to exit the liners, but that's just a guess.

@AbhishekPallipparagopakumar: Another interesting paper.

Beware, also pressure gaining combustors exist, in research and testing, not commercially in gas turbines.

The question you linked to contains the answer to your question:

the small pressure drop in the combustor is caused by friction

@mins: You have a restricted volume in a piston engine, while the volume inside the combustor is open at the rear end. Granted, there are some turbine blades in the way, but in general jet engine design is about restricting flow more at the front and less at the rear, so the air knows which direction to flow.

As somebody else stated, velocity increase shouldn't be connected with pressure loss, as when we say "pressure loss", we mean loss of stagnation/total pressure, not static pressure. So if velocity increases isentropically, total pressure would still remain the same. The (total) pressure loss in combustion chamber is mainly due to entropy-generating processes such as friction and turbulence.

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text:
Why was pitch angle protection not active in the CRJ 200 during the crash of Sweden Air 294?
I have read about the CRJ 200 Sweden Air 294 crash. I understood that the main cause of the accident was faulty IRU and wrong declutter PFD design. The human error also lead the aircraft into a catastrophic condition by not having good communication between the pilot and FO about a miscompared reading of PFD. But some questions are still buzzing my mind. The questions are below:

Is there any pitch angle protection in the flight control system of a CRJ 200?
Did the aircraft fly using autopilot when the miscompare happened? If yes, what is the reference attitude for the autopilot?
If the aircraft used autopilot, so when the pilot tried to push the yoke to pitch down the aircraft, did the aural alert of disconnecting the autopilot alarm the crew that the aircraft is in level off condition (not pitching up steeply). Also, did the CRJ 200 also use breakout force of yoke to disconnect the autopilot?

I am intimately familiar with that incident.  The airplane only had FDR recording the left PFD so they don't really know what was showing on the right one based on FDR.

The only pitch angle protection is the shaker/pusher. They didn't get that slow.
The AP runs off the Flight Director it's selected to.  This is normally the FD of the pilot flying.The  autopilot kicks off when the pitch attitude exceeds a certain angle (I forget what it is).  The capt was PF so the AP would have been coupled to the left flight director.
There is no yoke force mechanism for disconnecting the AP.  If the autopilot was in Pitch Mode and the PFD suddenly goes nose up it'll drive the elevator and follow up with trim inputs to keep the A/P servo loads in limits.  But in any case the AP will be in ALT Mode, the mode you are in once you capture and are holding an altitude.  It pitches to hold the altitude.  If the pitch indication goes nose up, but the altitude is not changing, it won't kick off until the pitch attitude exceeds the auto-disconnect attitude. Until then the AP will be holding whatever pitch attitude keeps the selected altitude.

The scenario was, the capt was sitting there, it's black outside, like black black, up and down, no lights anywhere.  He noticed his own PFD going "blue" (all sky).  Either he kicked the AP off or it would have kicked itself off when that PFD exceeded the auto kickoff attitude.  The airplane is just sitting there minding its own business in level cruise still.
Read the report here.  Capt panics and goes into tunnel-vision mode, and thinks they are in a zoom climb so he shoves the stick forward, putting them into a "bunt" (negative G pushover) in the pitch-black-in-every-direction sky.  The FO, (it was assumed his PFD was functioning normally but there was no FDR for it) would meanwhile have seen all brown on his PFD by this time (and on the Standby Attitude Indicator, but I don't think they ever looked at it).
So there you are as copilot: capt is all confused and has you both hanging in your straps with speed building and crazy roll attitudes to boot.  Your PFD shows all brown - diving.  It's black outside, everything that was on the floor is on the ceiling, and neither of you has a horizon; left side is all blue with the high pitch chevrons and display de-clutter happening, and the right side is all brown with the low pitch chevrons and de-clutter.  The noise is building to a crazy roar and with no horizon (all blue left and all brown right) it's hard to tell where the wings are relative to the horizon.  They both became hopelessly disoriented.
The did several rolls on the way down and hit the ground close to Mach.  There were no large pieces.
In my opinion there was a basic breakdown of a fundamental IFR skill.  When the Capt's PFD went weird, with no physical sensation to match, and no altitude and speed deviations to match, the FIRST reaction should be to do nothing, and cross check with the opposite PFD and the Standby ATT.  It's a case of the old saying, "Don't just do something, sit there".  Seeing the right PFD and the Standby working normally and the airplane's behaviour agreeing with what they showed, the capt should have transferred the AP to the right FD and made the copilot the Pilot Flying, turned off that display, and they would've carried on their merry way.
So bottom line is if the Capt had done nothing, they'd have been fine.  Even once the AP auto-disengaged due to the erroneous pitch attitude, the airplane itself would have continued level flight as trimmed.

Report summary page 9: instrument comparator caution not displayed in "declutter" mode???

Declutter clears everything but the horizon raster, basic pitch/roll references, and  the "up is this way down is that way" chevrons, to eliminate distractions while in an unusual attitude.  Situation they were in, they wouldn't have noticed the cmptr anyway. The OEM did experiments in the sim with unsuspecting pilots in recurrent and would cause the same fault to occur as a surprise.  Everybody did the correct thing, which was to do nothing initially, and assess. The 200 in cruise is VERY sensitive and snappy when being hand flown. It wouldn't take a very hard push to get 1G or more negative.

And the airspeed indicator and altimeters seemed to be OK.  It was a cargo run ...

Thank you for your answer, i would like to ask again several things

So the pitch angle protection was not like active pitch angle protection in modern airbus aircraft?

Thank you

No the 200 is an "old fashioned" airliner with mechanically operated, hydraulically powered flight controls.  The overall technology level is very similar to the 767.


text:
What are the applications, advantages and limitations of Gyrodyne rotorcraft?
Gyrodyne is a VTOL rotorcraft. It has ability to power both rotors and propellers for generating lift and thrust. What makes it of lesser popularity than helicopters. Are there any applications of Gyrodyne?
Wikipedia article

The compound helicopter similarly has a separate propulsor for thrust. The gyrodyne differs from it in allowing the lift rotor to autorotate without power during forward flight.
Both are capable of flying faster than a conventional helicopter, while retaining its VTOL abilities. It is thus an attractive idea wherever both high speed and VTOL/hover are required such as military, rescue and executive in-city applications.
However the extra weight and complexity of the thrust system make the already limited, complex and expensive helicopter even more so. Moreover the speed increase over a conventional helicopter is not great enough to be game-changing. Various programmes have led to several prototypes flying, of both gyrodynes and compound helicopters, but there are few if any applications where the high costs and reduced payload justify the modest extra speed over a helicopter.
The Fairey Rotodyne city commute gyrodyne flew but was then cancelled by the UK government.
Several compound helicopters such as the Lockheed Cheyenne have been developed for the US military but then cancelled.
When the USA wanted a fast VTOL military transport, they opted instead for a convertiplane, the Boeing V-22 Osprey. Its speed increase over a conventional helicopter has also turned out to be disappointing.
Maybe one day.

The noise of the Fairey Rotodyne had to be heard to be believed, apparently.

Indeed. Tipjets need to be cold to be quiet but AFAIK only the French ever got one into production, the Sud-Ouest Djinn helicopter.

Can a gyrodyne fly much faster than a helicopter, even theoretically? Unlike compound helicopter where the wings take over lift propulsion, in a gyrodyne the rotor still needs to spin, just via autorotation, so the limitiation that advancing blade must not reach critical (transsonic) speed and the retreating blade must move aft fast enough not to stall still applies, does it not?


text:
Is it possible to fly an EASA registered airplane with an ICAO license?
Is it possible to fly an EASA registered airplane with an ICAO license?
My problem is the following: I have obtained my ICAO PPL license in Argentina with 52 flight hours but currently I live in Poland and I'm trying to convert to EASA PPL. I know I need 100 hours for the conversion process but it is not possible for me to travel to Argentina and fly those remaining 48 hours.
Am I able to fly the remaining 48 hours in Poland with my ICAO PPL?

The ICAO doesn't issue licenses, so there's no such thing as an ICAO license. You have a license issues by the Argentine aviation authorities is ICAO compliant, which means it is recognized internationally, and you can fly Argentine registered airplanes anywhere in the world. It does not automatically give you privileges to fly airplanes of any other registration, so no you cannot fly Polish airplanes at this point.
There may be a way to do it, depending on the regulations in both countries. In some cases you can get a temporary license on the basis of your other license, or get some sort of other written permission. You would need to ask the Polish aviation authority what you need to do.

Yes, it is possible. But, not in the sense that you are thinking. As GdD has pointed out, ICAO does not issue certificate nor register aircraft. Individual governing authorities of sovereign states do that. An ICAO certificate is a certificate compliant with ICAO standards. ICAO will recognize it. But, another governing body does not have to necessarily recognize it.
However, you may fly an aircraft as the sole manipulator of the flight controls while an instructor giving instruction acts as PIC. This would be a great way to get a jumpstart on your instrument rating while striving to meet the 100 hour EASA minimum. Even if it may not count towards PIC time in EASA countries (since you do not have an EASA certificate, it would count towards your total time. EASA might even have provisions for flying supervised solos or actual solo with an instructor’s endorsement.


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Where are "standard taxi" instructions published?
Example: at KATL (Atlanta), the ground control sometimes gives taxi instructions as "standard taxi"; Where is that defined?

Delta 2732 27-Right Lima Charlie "Standard Taxi."

In that case, from a south ramp, the aircraft is noticed taxiing on Lima to 27R at intersection LC.
The question is, how did the pilot know that "standard taxi" meant going on taxiway Lima? Where are "standard taxi" instructions defined/published?

Please don't create a new question for this. You can edit your original question to add details, so it can be re-opened.

You can find a nice article on standard taxi routes here. They are included in the NOTAMS, or on Jepp charts if you have access to them. The full standard for publishing them can be found here.
This is what they look like:

(source: own image)
As ymb1 points out in the comments you can access them here as well.

Thanks for the response. It brings me back to my original question though. I don't have access to Jepp charts so I'm relying on Notices to Airmen only. In ForeFlight the current release of Notices to Airmen (Feb. 27, 2020) doesn't have any notices for Southeast United States. So, since Atlanta is in the Southeast U.S., there are no Standard Taxi Routes published for Atlanta. I was just wondering if anybody knew of anywhere else they might be published other than Jepp Charts or Notices to Airmen. I'm guessing they're not. Thanks again for the response.


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How did this flydubai 737NG get Max winglets?
I’ve seen this one on my way to the office in DXB. It’s clearly equipped with paired MAX winglets, however the engines are not curly. So judging by symptoms it’s not MAX. Was filming from a car, hence tail number is not visible. It’s A6-FEC, which, according to planespotters.net, is 737ng and 7+ years old. How did it get those winglets?

The registration looks like it ends in "FES" not "FEC" to me. Doesn't really matter either way, they are both 737NG's, only FEC is 2 years older than FES.

These are called Split Scimitar Winglets and they are offered as an upgrade for some existing Boeing 737 NG series aircraft:

Split Scimitar Winglets are offered by APB for the 737-800 and 737-900ER and came into service in early 2014. They are available as a retrofit to existing winglet aircraft.
A set of SSWs weigh 133kg (294Lb) per aircraft but give fuel savings of 1.6% on sectors of 1000nm rising to 2.2% on sectors of 3000nm. This equates to an extra 65nm range.
The modification requires a trailing edge wedge, strengthened stringers and ballast weight but no changes to any avionics or the FMC. The base price cost for an upgrade from blended winglets to SSWs was $555,000 as of 2014.

(b737.org.uk)
According to this article (in German), Flydubai is using this upgrade since 2019:

The low-cost airline from Dubai is equipping 30 Boeing 737-800s with so-called Split Scimitar Winglets. The scimitars on the wing tips save thousands of liters of fuel.
[...]
The first aircraft of the low-cost airline from Dubai - it bears the A6-FEC registration - has already been equipped with the split wing tips.

(translated by Google)
It is not exactly the same winglet as the MAX has (see also Why do newer 737s use two different styles of split winglets?) as you can see in the following images:

(Flydubai Boeing 737 NG, aerotelegraph.com)

(Flydubai Boeing 737 MAX, photo by Nabeel A. Hashmi)

Those have to be REALLY effective to be worth over half a million dollars!

@MikeBrockington If they fly 6 legs of 1000NM every day at 1.6% lower fuel burn, they save about 560kg of fuel a day. At $600 per ton, that is $336 saved per day, which means they save $555,000 after about 4.5 years. At 2 legs of 3000NM every day (which saves 2.2%), they already break even after 3.3 years.

I didn't notice the 1.6% / 2.2% initially, but even those numbers are surprisingly high - for comparison, that sort of change on a racing car would be the difference between first and last on the grid.


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What are the differences between FANS A, B, and C? Is FANS C commissioned?
For the Future Air Navigation System, what are the differences between FANS A, B, and C? Is FANS C commissioned?


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How does an aircraft maintain an orientation that was actually caused by a external disturbance?
What is the difference between centre of pressure, aerodynamic centre and neutral point?
At this link, there is an image used to explain the answer, but not much has been spoken about it.

I understand that the disturbance was caused by either the CG moving too ahead or too rear, or the CP moving forward of the CG. I would like to know that in the given image, how did the aircraft hold the disturbed orientation ?
Was it perhaps by mechanically shifting the CP back again using some device ?
Thanks in advance.

I think you'll be interested by the section about pitchwise stability of how it flies

thankyou @ManuH sir, i will look at it

Stability of the aircraft has nothing to do with control surfaces or moving CG to control the aircraft (that kind of aircrafts are very rare anyways). When researching or testing for aircraft's stability, control surfaces are either fixed to neutral position or they let alone to float freely, so control surfaces are not used to make aircraft more stable. That's of course true for conventional aircraft.
On the other hand you can produce an unstable or neutrally stable aircraft, however in that case you are required by regulations and nature to use some kind of control computers to keep aircraft in control all the time. MD-11 and Boeing 777 are two examples of this. Even though they are not unstable nor neutrally stable, they are definitely less stable than the requirements for the conventional aircrafts. To get away with that they have to have couple of flight control computers to keep the aircraft sane. However, even when the automation fails these aircrafts still have some positive static stability. How far you can go towards unstable side depends on design choices. You can further read Peter's post about why there is really less bang for buck when you further decrease the stability.
When statically stabil aircrafts are disturbed by any outside or inside forces (gusts, hitting control column etc) it  creates a restoring moment which returns aircraft to its initial position. That makes aircraft easier to fly.  Unstable aircrafts however tends continue to move in the direction of disturbance. So if a gust hits the aircraft and increases the AOA slightly, the aircraft continues to increase its AOA by itself and snap out of control eventually. That’s why you need flight control computers to stop any uncommanded movements.
The picture you show illustrates a neutrally stable aircraft, which means that it does not show any reaction to disturbances and maintains its disturbed position. Some aircrafts are designed that way to increase its maneuverability, reduce trim drag and increase fuel efficiency. Check out that link for a comparison of stable and unstable fighter aircrafts and how they behave during maneuvers. Some of these aircrafts are dubbed under different names such as relaxed static stability instead of calling them unstable or neutrally stable aircrafts in order not to freak out the masses.
Stability of aircraft is very closely related with CG position. As a general rule moving CG forward makes it more stable and moving aft makes it less stable and eventually unstable if gone out side of CG limits. Normally you won’t intentionally move CG out of limits but there are accidents which caused that. For example in this Boeing 747 accident at Bagram, payload got loose and moved aft of the aircraft uncontrollably during takeoff and aircraft become extremely unstable that no control input would be able to recover it.
These all are static stability. The dynamic one is another beast.

While having relaxed static stability, neither the MD-11 nor the B777 have anything approaching neutral or even negative stability. There is still some stability margin between relaxed and neutral.

Thanks Peter, incorpororating.

Your own answer is correct. You "mechanically shift the CP (in relation with CG)" with a control surface.
Perhaps this is easier to see on the roll axis, where we use ailerons to laterally shift the aerodynamic CP.  If the plane has dihedral, it will try to roll back up right, if not, it will remain in a bank, similar to your picture.
As a note to those "dihedral unbelievers", yes, a strong yawing or spiralling tendency will cancel dihedral stability, but that is an issue of the rudder.
A plane with "nuetral stability" stays where it is after control input or "external disturbance" is removed.

Sir, may i ask you a similar question in the case of missiles or rockets ? A missile moving at constant velocity which has side thrusters at the nose and tail end in an X configuration, where vertically opposite thrusters are fired to cause a torque. We know that if the CP is aft of CG we will face a resistance from the body as in a resoring moment, but the CP also moves forward of CG with increase in AoA. So how much force/torque would the side thrusters have to use to be able to change the orientation of the missile ? And then how do we hold it in case of missiles ?

Keep in mind air friction will slow any rotation after control input is removed.  But a missile, airplane, arrow, spear that is not directionally stable is difficult to control.  The javelin solves this issue by spinning.


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When does ATC contact the pilot for a frequency change?
Usually, when the aircraft enters a new flight information region for example, ATC will ask the pilot to enter a new frequency. I'm curious about when they do. Is there a rule about it (in an IFR situation)? I assume it may be different between EASA and FAA regulations.
Thank you.

I don't understand what  you're asking since you appear to have answered your own question. As an aircraft moves from one area of responsibility to the next the controller hands off communications to the next controller. This seems obvious to me. What 'rule' do you expect to find?

Well, I don't think that it is that simple in my opinion, someone should confirm it but maybe ATC have to anticipate this kind of event, to prevent a frequency change error from the pilot for example. I don't believe that they inform the pilot just when they "cross" the new area.

@FlyingRandomGuy They do - a combination of readback and use of names prevents errors. Pilots should know their route and who they're going to be talking to, so the new frequency shouldn't be a major surprise

The entire sky and all airports are divided into ATC areas of responsibility. Whenever a flight moves from one area of responsibility to another, the pilot needs to change frequency to talk to the next controller. A flight can only be under the control of one single ATC unit at any one time, which usually equates to being on one single radio frequency. When under ATC control, pilots do not change frequencies unless instructed to do so.
For the en-route phase, airspace is divided into sectors, defined as three dimensional areas. Each sector will typically have its own dedicated frequency, although sectors can be combined in which case several sectors may operate on the same frequency.
On the ground, depending on the size of the airport, there can be multiple different frequencies. It is common to have one tower frequency per runway, and then one frequency for the taxiways - or possible several, if the airport is large and complex.
ATC will instruct the pilot to change to the next frequency at the latest when the flight enters the new area of responsibility, and often a minute or two before that. At that point, the flight will already have been coordinated between the controllers, so the controller of the downstream area of responsibility knows it's coming. Specific rules for transfer of communication is agreed between adjacent ATC units in letters of agreement.
An example from Copenhagen:

AIP Denmark EK AD 2 - EKCH - AREA OF RESPONSIBILITY
Each color depicts an area of responsibility, and (this is a bit simplified but) essentially one specific frequency that pilots should be on when they are within that area. You can see that each runway (roughly) has one frequency, and the apron area where aircraft park has another. When taxiing from one area to another, the controller will instruct the pilot to change to the next frequency.
In the air, it can look something like this:

AIP Denmark EK ENR 6.2 - 3
The dashed lines indicate borders between areas of responsibility, and the bold text indicates the frequency to use in that area. Again, the controller will instruct the pilot to change to the next frequency when crossing from one area to another.
Further reading

Thank you for your interesting answer.

@FlyingRandomGuy Welcome to Aviation.SE =) Thank you comments are discouraged on this site. Instead, please consider up-voting the answer.

The controller will request the pilot changes frequency either when the controller is ready for them to do so:

G-ABCD, Contact Anytown Control 123.000

Or, they can request change at a particular moment, for example:

G-ABCD, at Waypoint Contact Anytown Control 123.000

or

G-ABCD, when passing FL100 contact Anytown Control 123.00

That's it really - there isn't some huge preamble or discussion.

Other answers have addressed where and why but perhaps not how or, as you asked, when. I'll answer that for FAA-land.
The transferring controller must transfer radar identification of the target before entering the receiving controller's airspace (for VFR aircraft) or protected airspace (for IFR aircraft, i.e. 1.5 or 2.5 NM from the airspace boundary). The process for transferring radar identification is spelled out in the 7110.65 chapter 5 section 4; you can do this physically (go to their scope and point at the target), using automation (enter a command to "flash" the target on their scope), or manually (call them and advise of the target's position relative to a fix).
The receiving controller "buying" the handoff means they have looked at the incoming target relative to their traffic and determined that they can allow entry into their airspace. If they need a restriction (altitude, speed, heading, etc) they can call the transferring controller to coordinate that.
The actual transfer of radio communications happens when the transferring controller has determined that, on its planned or assigned heading and altitude, the target will not conflict with any traffic in their own airspace and any entry into a third party's airspace has been coordinated (5–4–5 (c)). This could be tens of miles before the actual airspace boundary depending on traffic, aircraft speed, controller preference or technique, etc—but should be no later than the airspace boundary itself. It will generally be 2-5 minutes before the target actually crosses the boundary.

You should edit your answer to specify this is ONLY valid in the United States of America!

@pcfreakxx, see the very second sentence of the answer...

Great, thanks for editing! Good night :)

I didn't edit that, it was like that in my original.

In IFR flight the ATC controller will not tell the pilot to change frequencies until he has coordinated with the next sector. The next controller must check for conflicts before he can accept a new aircraft to his sector.
More and more this is done through Controller–pilot data link communications (CPDL) text messaging and no radio call is needed to tell the pilot to change frequencies.


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Why is the tail group of virtually every airplane swept instead of straight?
Even low performance airplanes like ultralights have their tail group (vertical and horizontal stabilizer with rudder and elevator) swept backwards knowing fully well that a straight tail group will produce more force than a swept tail group of the same area. Is the sweeping of an airplane's tail group simply aesthetics or is there some aerodynamic advantage involved?
The reason why I'm asking is because I'm trying to design and build an ultralight and was wondering if I can just build a straight rectangular tail group as seen below (for the sake of simplicity).

(source: fbcdn.net)

Get rid of "tryna".  Also there are PLENTY of aircraft with non-swept tail groups.  For example, most sailplanes.

You know 'tryna' is in the dictionary?..Urban dictionary.

There is more to it than just looks.
One immediate benefit is a more backward location of the center of pressure on the backwards swept surface. But that effect is small and has to be bought with a lower lift curve slope, i.e. lower effectivity at low angles of attack rsp. sideslip.
But once sweep is big enough, it will extend the useable range of sideslip angles at which the tail is effective. Sweep reduces the lift curve slope but extends its linear range to higher angles, so the maximum lift per area of a swept surface is about as high as that of an unswept surface. This is especially true for low aspect ratio wings where the outward movement of the boundary layer is not a big factor. Therefore, the aerodynamics of a vertical tail suffer much less from the usual sweep effects we know from swept wings.
Adding a fillet ahead of the root of the vertical tail increases this effect further and has been instrumental in making designs like the Boeing 307 spin proof. Before that change the Boeing 307 prototype suffered separated flow on the vertical in a spin and crashed when the aircraft oversped in an attempt by the pilot to end the spin by applying differential thrust.
While the wing operates in a narrow range of angle of attacks and straightens the airflow for the tail, so the horizontal tail is able to work within an even narrower range, the fuselage creates an unstable yawing moment over a much larger range of angles of sideslip. In order to have enough directional stability even at high angles of sideslip, a swept vertical tail is very helpful. Yes, this swept tail needs to be larger than an equivalent vertical tail which is designed for single-digit angles of sideslip, but this straight tail will render the aircraft unstable once it ventures into higher sideslip angles.
Reference: NLR Report A-1582. Sorry, I found no online source. It is discussed in Ed Obert's "Aerodynamic design of Transport Aircraft" on page 418.
Horizontal tails do not need the extended working range - here, it is enough to add stabilizer trim in order to adjust tail lift for different wing flap settings. Besides, building a horizontal tail with a swept hinge line is much more complicated than building a straight hinge line, so most horizontal surfaces have just a little sweep such that taper and sweep together result in a straight hinge line.
But there is one exception: In the early 70s many glider designs used a full-flying, swept horizontal tail, like this Standard Cirrus below (picture source):

This is obviously not for compressibility. By sweeping the tail its center of gravity can be moved close to its center of pressure, so this tail needs no mass balance and has low actuation forces. The downside is the rigid, symmetrical airfoil: At low speed and higher angle of attack it has very little effectivity because the flow stays separated while a conventional tail with a fixed stabilizer will already show attached flow. This led to a number of fatal crashes in winch launches when the aircraft would pitch up into a stall and could not be controlled.

I've flown an LS-1 which has the same tail and which flew great stick fixed, but stick free, having no anti-servo tab, it seemed to get pretty much all of its static stability from the trim bungee.  Stick free it was slowly divergent, and I felt that without the bungee providing some centering force it would have been all over the place stick free. I let it go while eating a sandwich once, and eventually it was diving to Vne and pulling up to near stall even though it was trimmed to about 60kt.Perhaps the bungee was weak.  Since you don't actually fly them that way, it wasn't really a problem.

@JohnK: Yes, flew an LS-1f myself (but not often). You are right about that bungee. Since you could fly a classic phygoid without falling into a spiral dive first, at least lateral stability was pretty decent ;-)

I really enjoyed flying it. Then it was crashed following a mid-air.  The characteristic I really liked was that full aileron and full rudder applied at the same time gave a more or less coordinated roll, making the initial crank and bank turn-in when you found a thermal effortless.

@JohnK Then you flew it just at the right speed. Normally, the adverse yaw gets smaller when you fly faster, so less rudder is needed.

This is a must read, and the horizontal stabilizer can benefit too from front leading edge sweep for stall recovery.  Amazing how many things the 1910 Etrich Taube had right.

There is no doubt some aerodynamic benefit to sweeping tails on high speed airplanes, and there is some benefit, as Zeiss says, in that there is a modest increase in moment arm without lengthening the fuselage (on the other hand, the sweep imparts a small pitching moment when the rudder is displaced, but it's not enough to be a big deal).
At any rate, on just about all lower speed aircraft, especially GA ones, it's really just "styling"; one of the only places in aircraft design where form supersedes function.
In the early to mid 60s Cessna changed the vertical tails on their models from straight to swept.  This had absolutely no effect on performance.  It was pure styling because a swept tail looked more "modern" (It's also the time when they came out with silly marketing names like "Land-O-Matic gear".. you know, spring steel leaf or rod gear legs).  Meanwhile pretty much all horizontal tails have remained straight.  Why?  Nobody cares how it looks from below.  It's all about the profile.
So if there is a major technical benefit to sweeping a tail on a particular design, you can generally expect to see the horizontal tail also swept.  Otherwise, styling.

Horizontal tails stayed straight because a straight hinge line is much easier to build than a swept one. On a vertical which extends only to one side this makes no difference, but once there are two sides that need to meet in the middle it is better to keep them straight.

Nonetheless, if there was significant benefit beyond looks they would have swept horizontal tails. The only low speed airplanes I can think with a swept horizontal tail is the Aerostar, and IIRC, the Swearingen homebuilt and in those cases I expect they were going after a little bit of extra arm.

@Peter Kämpf: Horizontal tails don't need to meet in the middle on most GA aircraft. They generally have left and right sections separated by the fuselage, so it would be possible to have them be asymmetric.  I'd guess that a more important factor would be allowing a single straight support beam that passes through the fuselage

@jamesqf: Like a wing, they need a spar. Swept spars are heavier and harder to build (added torsion at the root). Also, it helps a lot if both sides of the elevator have a mechanical connection. Otherwise an antimetric mode of the tail can couple with fuselage torsion and cause flutter. Doing this with a cardan joint is more complex and adds another failure mode. It is just not worth it.

@jamesq actually the vast majority of GA horizontal stabs have a single spar running across with either separate structures forward of the spar pinned to the sides of the fuse, or the entire stab surface as one box structure (like on a172).  To make a stab spar or box in 3 pieces is much heavier for negligible benefit.

@John K: My bad.  I'm so used to the Cherokee's stabilator that I tend to forget that a lot of other planes have tail surfaces that bend in the middle :-(

One reason is to save weight.
It goes like this: the further to the rear the tail surfaces are, the smaller (and lighter) they can be, but fuselage structure is heavy.  If you make the surfaces swept, the area is moved to the rear, but little if any weight is added compared to unswept surfaces.
Beyond the actual weight saved at the tail, we used to say in model building that "an ounce at the tail is worth a pound at the nose."  That's because of moment arms; a tiny amount of weight in the tail may require a very large mass of structure (or even ballast) near the nose to keep the center of mass where you need it for stability.

Smaller planes: Marketing. Look at Mooney, straight tail, vs Cessna/Piper/Bonanza. All went to swept tails because it looked faster.


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Why aren't there any larger autogyros/gyrocopters?
Simply put, all the information I've found about autogyros/gyrocopters has been about very small single-engine sport aircraft that can carry the pilot and maybe one passenger.
Why aren't there any larger autogyros, with a scale along the lines of the larger helicopters or twin-engine GA airplanes? Is there a fundamental physical problem stopping you from ripping the wings off a twin-engine light aircraft and sticking on the helicopter blades of an equivalently-sized helicopter to build a gyrocopter that can carry a dozen or so people?

Check out the https://en.wikipedia.org/wiki/Fairey_Rotodyne

The Fairey Rotodyne's history suggests that the problem isn't mechanical or physical, but convincing someone to pay for it.  When it's that big, it's not a fun toy anymore, it must earn its keep.

Why aren't there any larger autogiros?

Because you would basically have a machine with the same limitations of a helicopter (in terms of speed and maintenance) but, since the rotor of an autogyro produces only lift, you'd need to add one (or more) propeller for forward propulsion, a tailplane for stability and controllability and a wing to offload the rotor at higher speeds.
Or vice versa, because you would basically have an airplane with the addition of a free-spinning rotor that would add further weight, complexity and speed limitations to it.
And if you would go for a gyroplane instead, like the (in)famous Fairey Rotodyne, then the matter would be even more complicated since the rotor wouldn't be free-spinning like in an autogyro rather powered and controlled like in a helicopter... the apotheosis of the complexity is served.
In the end an autogyro makes sense if you want to add safety to an aircraft that doesn't need to be fast or big: should the engine stop, it can autorotate till zero speed, while a conventional aircraft couldn't fly slower than its stall speed.
If you need to go fast and/or big then a tiltrotor like the Valor or a rigid coaxial rotor like the Raider is definitely more efficient design.

What about passenger service to bush airports with runways too short for larger GA aircraft? I remember a bit of controversy last year here in Australia when CASA stopped flights to a few islands because the runways were too short for the larger aeroplanes that were now being flown and then someone drowned on a boat ride to them.

How far are those islands from the mainland? And how many passengers should be served? I suppose that something like a Super Puma might do the job (?)

I think the comparison to helicopters / airplanes is a bit faulty: in fact when compared to a helicopter you trade tail rotor to a forward propulsion propeller. You have the benefit of not needing main rotor gearbox, which is a major weight/ maintenance benefit. In comparison to an airplane, you trade main wings to the rotor, which I imagine is a pretty equal trade.

"In comparison to an airplane, you trade main wings to the rotor, which I imagine is a pretty equal trade" It's not: a rotor is a much more complicated part, it needs flapping and lead-leg hinges (read: maintenance), its structure must be resonance-free for all the rpms at which it can rotate (read: complicated design and more weight) and it... rotates (read: vibrations, which might set in resonance the airframe, so again more complicated design and weight) ...

... "when compared to a helicopter you trade tail rotor to a forward propulsion propeller" It depends: on the Fairey Rotodyne the tail rotor was substituted for a quite complex and noisy system ejecting fast and hot gases from the blade tips (and this system was actually the reason that commercially killed this aircraft). Furthermore the tail rotor in an helicopter is used also for manoeuvring around the yaw axis so it actually substitutes also the vertical tailplane.

Simple supply and demand. There just aren't that many people interested in large autogiros to justify the costs of producing and supporting a certified aircraft.


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What is the theoretical maximum RPM of a typical aircraft piston engine?
Given a standard 6-cylinder, direct-drive, horizontally-opposed engine like the Continental IO-550 or Lycoming IO-540, the maximum RPM for those engines is 2700 RPM. That's due to keeping the propeller tip speed under the supersonic range.
But what is preventing these engines from turning at a higher RPM for another, non-aircraft use?
I'm thinking if they would work up to around 5000 RPM or so. Maybe the fuel mapping must be modified? Will the valve-train start to float at that RPM? The application would be automotive, so the load would be far, far less from a duty cycle standpoint than an aircraft application: basically, 5000 RPM would only be seen for a second or two at a time under full (or nearly full) load.
Is there anything else I'm missing? I realize this is a weird question, just doing some thought experimenting.

Engines are typically geared to max the prop at 2700 RPM for the reason you describe - and instruments typically show prop RPM, not engine RPM. It doesn't mean the engine is running at that speed at all.

@falstro: Typically?  In my experience, most aircraft engines are direct drive.  Gearing is the exception.

@jamesqf I typically fly exceptional aircraft. ;) Jokes aside, I'm sure you're correct. I did my training in the DA20 with Rotax, which does have a gearbox. My flight school was also primarily focused on Rotax powered LSAs like the Ikarus C42, my guess is that most of them have gearboxes which would explain why it was mentioned during ground school. The instruments still show prop RPM though, not engine RPM.

Size related issues.  A Cox 0.049 cubic inch aircraft engine will spin 20,000+ RPM, smaller engines potentially even faster.

GTSIO-520s, if I recall correctly, turn at 3,300rpm.  The reduction drive takes the prop to 2700ish.  So...at least 3300rpm.

There are three factors which limit the possible speed of piston engines:

Flame speed in the fuel-air mixture,
relative speed of moving parts, here the pistons in their cylinders, and
Valve inertia and valve float.

If the engine runs too fast, the flame front originating from the spark plug will not have traveled far enough to have burnt most of the fuel by the time the piston moves down again. This puts a fundamental limit to the growth in power output over speed in piston engines.
Also, if the relative speed between moving parts is too high, the lubrication will fail and the parts will overheat quickly. In order to run at the highest possible speed, rotary engines used castor oil, which in turn motivated early aviators to wear long scarves over their mouth so their digestive system would not be compromised by sitting right in the exhaust stream of their engine. Today, lubricants have improved but still set a clear limit to the maximum speed at which a piston engine can be run. Cooling can be managed by pressurizing the cooling system and improving radiator and pump performance while inertial loads on the engine components can be dealt with by lightweight, high-strength materials.
Reducing the bore will allow a higher speed before the ignition limit bites while reducing the stroke will reduce piston speeds, again allowing a higher engine speed before lubrication fails. An optimimized engine will balance both so that the possible speed can be fully exploited. For the IO-360 and IO-540, those dimensions are 5⅛" and 4⅜", respectively. This places them below the last generation of big aviation pistons and closer to the typical interwar engines.
With higher speeds, the valves need to move faster, too. If the force of the valve springs are not sufficient to close the valves quickly enough, compression will suffer, limiting RPM and power. In order to reduce the inertia of each individual valve, the number of valves can be doubled or even tripled.
I could not find reliable data on the engine speed of Reno Air Race winners, which should come close to the maximum sensible engine speed at that size class. The best I could find was the 3,700 RPM of the Jumo 213 E, an engine with 5.9" bore and 6.5" stroke, so I would guess by using good fuel and lubrication, the Lycoming might end up somewhere between 4000 and 4500 RPM. I'm sceptical that much useful power can be extracted at 5000 RPM and am sure that the lifetime at this speed will be measured in minutes, not hours.

I'm rather skeptical about the lubrication part.  After all, smaller piston engines like motorcycle engines can redline at well over 10K RPM.

@BaileyS I'd assume that aero engines use different oil because they're lower-revving, rather than because there's something about aviation that means you couldn't use an oil that would work at 10k rpm.

@Bailey S: I think you have cause and effect reversed here.  Aviation oils have the characteristics they do because that's what conventional aviation engines need.  If you built an experimental using a high-revving motorcycle engine, you'd use the kind of oil the  manufacturer specifies, not aviation oil.  IOW, it's not anything fundamental to the oil that limits IC engine RPMs to 2700 or so.

@jamesqf: Do the numbers yourself. Engine speed and stroke are inversely related precisely because piston speed is limited by lubrication.

@Peter Kämpf: Maybe so, but that lubrication limit is far above the speed of typical aircraft engines, as demonstrated by the fact that there are many engines  (of similar displacement, too, so it's not just a size effect) that do run at much higher speeds.

@jamesqf: I agree, this is true today but was a limiting factor historically.

@Peter Kämpf The other posters are right. Right off the top my head I can think of the Yamaha Genesis engine line for the R6 and R1 sport bikes.  The 599cc engine in the R6 had a redline of 16,000 RPM!

@CarloFelicione The stroke of the Genesis is 44.5 mm (and the redline is 15,800 RPM). Compare that to the 165 mm of the Jumo 213 and RPMs should have a factor of four between them. Looks about right, given the better performance of modern oils. Also, using three intake valves with their lower inertias helps, too.

I had a 2.0L car engine (Honda F20C) that redlined at 8100 RPM, so high speeds are certainly possible with standard automotive oil. I don’t know if you could extrapolate the other issues from there to a 9.0L IO-550, though.

Valve float can be solved with pneumatics or hydraulics - look at the V12 & V10 Formula 1 engines from the 2000s and early 2010s. They ran to 22-24000 RPM. Even current F1 engines (with much lower red lines a mere 14-16000 RPM) still use hydraulically operated valves.

@FreeMan What was the life time of those F1 engines? Would you trust your life to one in your plane? You are comparing apples to oranges (or maybe pumpkins, who knows)

Um... Well, this season they're expected to last about 7 races @ ~300km per race (plus practice and qualifying sessions). Yes, I'd trust one, but only for a short trip. ;) My point, though is that while the issues you specify are real, they can be overcome if one throws enough time, money & engineering at it. Probably not with an existing aviation engine, though.

The size and weight of the pistons is going to be a major hurdle. With a 5.25 in bore and a 4.25 inch stroke, the pistons are massive and don't change directions very easily—there's only so many Gs you can put a shape this large through at the top and bottom of each stroke before the metal starts deforming. Bounce an open umbrella up and down really fast, and you'll start to get the picture.
Cooling would also be a major factor for non-aviation use. Aircraft engines (more or less rightly) assume that there's going to be a large fan out front and/or 100+ mph of airflow. Liquid cooling would allow the heads to maintain a more constant temperature, but would also add weight and complexity.
If you want a faster-revving flat six that will put out more than 100hp and is suitable for automotive use, I might suggest pulling an engine out of a Honda Goldwing or Valkyrie. Given the edited description, though, I'm guessing you're thinking of a drag racer.

those super big block V8's based on the chevy 454 ( I think it was as 630 something cubic inch ) had a bore of like 5.0 and stroke of 5.8 and they turned up to 7200RPM.  Obviously race built and highly specialized parts, but its been done :)

I agree with the other posts with the general limiting factors being failure at high rpm and cooling being a problem. Assuming reliability isn't a concern for you... what else will be the limiting factor?
Reliability and cooling aside no-one seems to have mentioned intake restriction or valve train.
The first limiting factor will be how much fuel can your engine injest and burn. So is the engine normally aspirated or forced? NA engines are limited by how much fuel and air they can draw in. So: carbs, intake manifold, cam and valves need to be able to flow enough to produce the power you want.  Forced induction makes this a bit simpler.
But as revs rise to produce big HP numbers you are going to hit the glass ceiling of how fast your valve train can function. At some point the valve springs will not be able to close in time (known as valve bounce) and can simply stay open. This affects the  compression and combustion strokes and may result in the piston hitting the valve shortly followed by very unpleasant noises.
My answer was given with a stock aero engine as the starting point, thinking about what limitations you would hit as revs rise. Each limitation can be overcome but the solutions get more complex and expensive as revs rise and you chase bigger HP figures.

yeah, valve float was one of my first concerns.  and I was thinking turbocharging.

Yep i agree. But considering OPs question, I tried to answer with a stock aero engine as the starting point.

There is nothing physically limiting it but the engines are designed to run optimally in the given range so they may simply not run very well. Of course you could always change the cam timing, spark timing etc. For the record your run of the mill aircraft engine is not all that different than the early Porsche/VW air cooled flat car motors (which were even used on aircraft at one point). You would need to cool it at least partial with an oil system and partially with an air fan much as Porsche did on their pre 996 era cars if you did not want to leverage water cooling (and you dont need to). For the record large bore air cooled engines can develop a lot of horse power and rev very high if built correctly.
For what its worth aircraft engines are far more expensive than their non FAA certified automotive counterparts and you are better off using a car engine simply from a cost perspective.

yes, plans were to mimic the 911 style cooling with shrouds and fans, and lots of oil capacity and cooling.

The Porsche Mooney you mention had an engine based on the 911, not the 356/VW.  2 extra cylinders, a LOT more horse power, and in later years, higher RPM limits.  RPM orange line on my '65 356C is at 5k rpms (and the car is cruise-able at near that), redline is at 5500 and you are booking an engine rebuild at 6k.  On the late 70s/early 80s 911sc redline was closer to 7k IIRC...

@ivanivan both the 911 3.2 motor and the earlier 356 era 4 cylinder were actually certified for flight. The 4 cyl was used iirc on blimps and yes the Mooney had the 911 motor with an added stepper gearbox for the prop.  The redline on my 78 911SC is 6200 RPM but in 5th I am around 3.5K on the highways. 911 Engines with their over cautious bearing setup can be built to redline even higher than that.

@Dave yup.  The 3.0sc and 3.2 "Carrera" (real Carreras have 4 cams!) engines are darn near bullet proof.

@ivanivan that they are...

There are mechanical limits to rpm and volumetric efficiency limits to engine RPM.
Mechanical: Piston speed- damaged piston, rod
            Piston acceleration - ring flutter failure
            Valve float- catastrophic valve failure
            Increase RPM results in higher oil temps
Volumetric: Ability to intake air is limited by:
                  Airflow limits of intake system:
                      carb
                      airbox
                      Intake tubes
                      Intake manifolds, and ports, valves, cam design and
                      timing.
All thees things determine the amount of air the motor is able to intake and that determines the rpm the motor will work best at. More details can be found by looking in a superflow flowbench manual available for free on the net.
Exceed mechanical limits and experience catastrophic failure. I the world of racing I often found mechanical limits by  exceeding them.
Exceed volumetric limits and see loss of torque.

But what is preventing these engines from turning a higher RPM, for a non-aircraft use?

Overheating.
It is important to remember that aircraft engines must be reliable enough to maintain enough airspeed for flight.  It is also important to understand that thrust is proportional to the square of RPM, so the operating RPM range is not going to be nearly as wide as a motorcycle or a car.

it is the drag of the prop that limits RPM.

For example, an aircraft may maintain level flight at 1500 rpm, but doubles its engine output torque requirement at 2300 rpm to climb.
A more practical solution to boost power output is the turbocharger, allowing far more horsepower at a lower RPM, while the "Genesis" motorcycle is screaming 12,000 RPM to make 120 horsepower.
Using an aircraft engine for a high RPM application is a bit like bringing a Clydesdale to the track and racing it against a Thoroughbred.  Generally not a good idea.

Niels responds to an old question.
Pushrod valvetrains in big engines (~500 cubic inch class) limit out at about 5000 RPM. Going faster than that usually requires an overhead cam and might yield ~6000 RPM, but past that the reciprocating mass tends to make the engine explode unexpectedly, so to go still faster (and make more power) you reduce the piston size and the crankshaft stroke and add more pistons to maintain displacement.
So instead of a 6-cylinder engine you now have a 10-cylinder engine, and you might make that monster spin faster with dual overhead cams instead of singles. But now you run out of lubrication capacity in the main bearings, so you re-engineer the engine for roller bearing mains.
Now you have to re-engineer the heads for higher heat-rejecting capacity so you do not overheat the exhaust valve seats, which means water-cooling and perhaps also forced-oil cooling.
Now the engine requires supercharging to overcome its pumping losses, so you bolt on a blower to make it spin faster and make more power... but all of this produces a big problem, as follows:
Every crank revolution wears the piston rings, bores, valve train components and crank bearings a tiny little bit. The useful lifetime of the engine is set by how many crank turns you can accumulate before the wear limits are hit. And this means that if you gear the engine down to spin the prop half as fast, you'll accumulate crank turns twice as fast per hour of flight time and you cut the TBO in half- and now you have to overhaul the gearbox and the supercharger as well as the internal engine components in 1000 hours instead of 2000 hours.
Drag-racing engines can push to 7500 RPM or sometimes 10,000 RPM and produce a thousand horsepower or more out of 500 cubic inches, with a TBO of several minutes (no kidding!)- and crowd-pleasing (i.e., truly spectacular) failure modes if any little thing happens to go wrong. So...
High reliability and long life dictate minimizing RPM's and engine complexity, so in internal combustion aircraft engines you stick with big pistons, direct drive, natural aspiration and you live with half a horsepower per cubic inch of displacement at sea level.

Really interesting! Not at all an answer to the question, but an enjoyable read nonetheless.

One could come up with a higher revving aircraft engine and gear it down for subsonic prop operation. That is what Porsche did with its PFM 3200 aircraft engine: took it's 911 flat six and geared it down. While it was a very good engine, with about twice the HP of similar displacement aircraft flat sixes, and was used to equip the Mooney M20L, it was also expensive to buy and had a fairly short TBO. Supposedly, the PFM 3200 sounded magnificent on takeoff.
Porsche exited the market in 2007 after $75 million in development costs to produce and sell around 80 engines. Supposedly, they bought back all of the PFM 3200 engines in use for liability reasons.
In contrast, the Continental and Lycoming flat sixes are much simpler, slower turning pushrod engines, built with an emphasis on reliability, not power to weight. Low RPM means no gearbox to gear down for prop operation, and no gearbox to maintain or fail. They are intended to operate at high power output for long periods of time without failing, as opposed to automotive engines that tend to loaf along at low power output, with an occasional burst of full power. Loss of power in an aircraft is a bit more serious than loss of power in a car, hence the emphasis on reliability.
So, if you want a flat six with lots of HP for non aircraft use... don't look at aircraft engines, unless you want an engine that turns slow, that you can floor for an hour or two regularly.

Porsche also had the "industrial engines" based on the 356 engine, for generators, pumps, watercraft, and even aircraft in the 50s - see http://derwhites356literature.com/New356Stuff/PorscheIndustrialMotors50s60s.html


text:
What needs to be considered when changing a tire during boarding/deboarding?
Passenger aircraft tires are physically inspected by the cockpit crew member or technician after each landing or before take-off, that the tire may have been cut or punctured as it may have hit something on the ground (FOD) while taxiing. If the tire needs to be replaced for any reason, the tire is lifted with a jack in the parking stand and the tire replacement is carried out less than half an hour (similar to changing a car tire).
Since airline companies are commercial enterprises and the time the aircraft will spend on the ground cause extra cost, can the tire replacement and passenger boarding/deboarding and/or cargo offloading/onloading operations be performed simultaneously?
What needs to be considered in order to replace the tire and perform the other mentioned operations safely at the same time?

Cargo onloading offloading could be simultaneous during boarding or debording  in particular when it concerns passengers luggage. However the maintenance team cannot not do any possibly invasive action during passengers boarding. Lifting is not allowed during passengers movement.

I have never seen an airline (or the military) have a maintenance procedure where a tire can be changed with pax on board the aircraft. Normally, if the problem is found when pax are on the aircraft, they are asked to deplane, the maintenance is done and the pax are then boarded once more. The biggest reason is that pax moving inside the aircraft can cause the aircraft to move and the jack to tilt and cause the landing gear to hit the ground. Without a tire, that could be really bad news.

I stood on the tarmac at Ben Gurion TLV/LLBG and watched them change a tire on an El Al 747 prior to departure. My dad and I were the last two to board and we were walking our dogs prior to putting them in their crates prior to being loaded for the flight to JFK. They got an extra long walk. The plane was full of people at the time. This was in 1984, so procedures may have changed since then. (Despite the incredibly high security that El Al has always maintained, I'd imagine security procedures wouldn't allow us out on the tarmac these days, either.)
Therefore, yes, changing a tire can happen while passengers are boarding. Whether it is Standard Operating Procedure now (or if it was even SOP back in 1984) I don't know, but I can vouch that it has happened at least once.

That was 35 years ago. I hope they have become more professional and safety conscious in the intervening time...


text:
Can Private Pilot training, funded by employer, count as company hours?
My employer would like me to get my Private Pilot License, and is funding the remainder of my training. The intention is to have me do my training on company time.
I am an engineer, and sit in the copilot seat of aircraft we test while collecting data. A commercial pilot actually flies, but for safety's sake, they would like me to have my private license while doing testing.
Could this potentially breach the commercial limitations of a Private Pilot license, as I am "technically" receiving compensation (my salary) while flying on company time? Or, as this salary is already being paid to me for my actual job duties, would the salary not be considered a contributing factor?
(For example, plan is to instead of working 40 hours/week, I would work 30 hours/week, and fly for 10/hrs/week)
If this would be a violation, would the solution to instead be to continue working 40 hour weeks, and accomplish those 10 hours outside of company time?

Welcome to Aviation SE!  This is a good first question!

Possible duplicate of What is the difference between "flying in furtherance of a business" and "flying for compensation"?

@TannerSwett I don't believe it is a duplicate, though it's "related". I responded to your answer with clarification as to why.

What is your employers goal with having you get your PPL?

@RonBeyer For safety purposes, as I go on test flights to monitor data readings, flight performance, etc. That said, I am not the pilot - I sit in the copilot seat.

Voting against closing... the other questions is essentially, "as a private pilot, can I do ___?"  This question is, on the other hand, "as a student pilot, can I ___?"  I think questions about who can pay for your training to become a Private Pilot, are sufficiently distinct from questions about what you can do once you ARE a Private Pilot, that this is not a duplicate.

What plane is it? Does it required two pilots at the control?

No law against this. Nor is there any restriction on who pays for your flight training. You are referencing something which applies to your privileges as a student pilot. You may not act as Pilot In Command (PIC) for compensation or hire, nor carry passengers or cargo for compensation or hire - see §61.89. Having an employer pay for your flight training cannot be viewed this way. Again, these regulations are only applicable to time as PIC, so, as a student, this would be only solo flight time.
Now, if the employer attempts to have you perform flight duties in the furtherance of their business while you are a student pilot, i.e. they asked you to ferry an airplane for them somewhere, or perform some other task which is not related to your flight training, that does violate the law. However, the employer only paying for you to undergo flight training is not a violation of federal law.

But presumably, the employer is receiving some benefit in this situation, or else they wouldn't be offering the deal. So in this scenario, the pilot is flying, the employer is receiving benefit from the flying, and the employer pays the pilot for the flying. Is that right?

@TannerSwett I am an engineer, and sit in the copilot seat of aircraft we test while collecting data. A commercial pilot actually flies, but for safety's sake, they would like me to have my private license while doing testing.

@CarloFelicione - My question though refers specifically to the fact that my training is not only be covered, my training hours are also PAID hours, that would count as party of my weekly hours. So, I am "receiving compensation while flying", which to my understanding is not allowed. Maybe I am wrong, which is why I ask.

That all depends. It will be necessary to see how your flight training promoted or improved your employers business before one can make such a decision. And incidentally that would only apply to time served as PIC only, which in your case as a student pilot would be solo time only.  All other flight training activities are not covered under those regulations.

I would bold the second sentence of the second paragraph. Only an attorney with a good background in the appropriate regulations would be able to give reasonably good advice in this specific situation.

If it was a problem then how could an airline hire someone off the street and give them paid training? Until they get their CPL they can't fly for hire, so if they considered training as compensation an airline would be unable to do this.

Read the regulations carefully here, people.  Those restrictions are applicable only to PIC duties and not flight instruction.

I've selected this as the best answer, but I do think linking to sources regarding these regulations would be beneficial.

@CarloFelicione but you need PIC time before getting the PPL. This is definitely a situation where a visit to a lawyer or the FAA is beneficial.

Ben as I described it, The only contention here would be on logging solo time.  Consulting with an aviation attorney would probably be a wise choice, however it would probably go into the boundaries of more of tax law versus aviation law.

No, there is no law to prevent your employer from compensating you for flight training or future work as an engineer - so long as you are not acting as PIC for a commercial flight.
We can give this a test by asking, "Does a doctor, nurse, news reporter, etc, need to have a commercial pilots license in order to perform their duties while in an aircraft and being paid by an employer? Of course not!
Being paid to train is entirely different than being paid as PIC for the carriage of passengers or goods. Another good example is many aircraft have load masters or older jets may have mechanics travel on all flights - they don't need a commercial pilots license either. It's only if you are the PIC (or co-pilot of a multi-crew aircraft).
Some 3 crew aircraft require an "engineer" (manages fuel, pressurization, etc) and he does not have to be a pilot or hold a commercial license.

Aircraft that require a flight engineer require an FAA flight engineer's license... They don't differentiate between commercial/atp for that one though.

A flight engineer, mechanic, nurse, or doctor all require certificates, but do not need a "commercial" license and has nothing to do with whether the flight is a private or commercial. Only the pilot and copilot matter. I use to be a "flight mechanic" on B-727. All I was was a paid A&P employee that road with the airplane. It is still common for older aircraft such as B747 to have mechanics with them in foreign countries - no commercial license is needed.

@jwzumwalt Good answer, but I am unsure how the example in the second paragraph relates? Could you elaborate?

@matt - The point is: you can be paid to be in the aircraft and still not need a commercial license. The commercial license requirement is only needed if you are the pilot or co-pilot.

@jwzumwalt Are you talking about an inflight doctor/nurse/reporter? Even if that is the case, what I am more concerned with is the fact that I will be getting paid when I am pilot (during solo time), or copilot (during instruction). I understand that after the training, there's no question that I would be fine.

The FAA clearly defines what a commercial flight is. A student flying a plane is not a "commercial" operation - it is "training". An instructor needs a commercial license but the student does not. The FAA does not consider a pilot taking customers on a flight to sell airplanes - as commercial. You are being paid to sell not fly.

@jwzumwalt I just don't entirely understand that reasoning, because I am being "paid to fly", though not for cargo/passengers.

You are not being paid to fly from the governments perspective. If that were the case than all the youth grants for learning to fly, or the airlines paying people to become pilots would be illegal. You need to start viewing this from the governments view point and case history. It is similar to student doctors being allowed to operate on people but they are not allowed to "practice" medicine. One is training, the other is for business.

Let us continue this discussion in chat.

You're not receiving compensation (salary) while flying on company time, because you're not "flying" … for 30 hrs/wk you're collecting test data as an engineer whether you have a Private license or not, and for 10 hrs/wk you are receiving flight instruction under the supervision of a qualified Flight Instructor.  You cannot claim any of those hours as flying as PIC under the privileges of a pilot license, so the question of flying for compensation is moot.
The fact that the company is financially supporting your education as a Private Pilot, believing it to be of supplemental value in performing your job as a Test Engineer, doesn't interest the FAA.
But it could violate IRS rules and trigger an audit if tax liabilities on reimbursed education cost and time as reported on tax returns by employer and employee don't align or are improperly calculated.


text:
What is this vintage small airplane with low wings and twin propeller engines?
Could anyone help me to identify this vintage aircraft, that can be seen in the background of this photograph, please?

The photo is probably from the 60s, as the car is a 'ZAZ 965', a Soviet copy of the 'Fiat 600'...

It's a LET L-200 Morava, a Czech plane...
http://www.aviastar.org/air/czech/let_l-200.php

The props in the original picture appear to have two blades, while the props on the picture on that site you linked has three. Is that simply a different configuration?

It's morava refinement: The original production model was superseded first by the generally similar L-200A, with more powerful Walter M 337 engines and, subsequently, by the final production version, the L-200D, which was introduced in mid-1962. This differed by in-corporating improved systems, strengthened landing gear, and three-bladed constant-speed propellers.


text:
What is the use of this jet aircraft with tanks between biplane wings?
Looking at this soviet-like aircraft:

Source
It looks like a turbine engineer team met a biplane aerodynamicist team to create this strange aircraft! More over, it appears the two big pottery pieces are actually tanks.
What is the story and the use of this jet aircraft?

Despite looking like toilets, I'm fairly certain the tanks are not pottery. :)

@egid, these were considered "bog standard" at the time. :)

From the source page the image caption is 'Samolot PZL M-15 Belphegor (fot. Autor)' - indicating it's a PZL M-15 Belphegor. (Yeah, I know there's already an accepted answer, but it was fairly simple... Didn't even need to be able to read Polish. :/ )

did you grab this from me off of Facebook? I posted it there yesterday.

identical image https://www.facebook.com/groups/41407135412/permalink/10158045611150413/?comment_id=10158050826265413&comment_tracking=%7B%22tn%22%3A%22R6%22%7D

for some reason it doesn't expand. posted by Bob Pasker Dec 6 @1:57

It is the Polish PZL M-15, as you can read in the image if you zoom in. From Wikipedia:

The aircraft was designed in Poland in response to a Soviet
  requirement for a new agricultural plane.

Agricultural airplanes fly slow and having a shorter span increases the number of (air)fields you can land on. That's probably why they decided using a biplane design.
The two tanks outside the fuselage could have several reasons:

Placing the chemicals further away from the turbine and pilot
Reduce the bending moment at the wing root
Shorter pipes between the tank and the spray nozzles

All this, of course, at the cost of a lot of drag. As explained in the image source page, fuel consumption was three times larger than other agricultural airplanes and it had a really bad maneuverability.
The jet engine was a requirement dictated by Aeroflot, who wanted to use the same type of fuel for their passenger and agricultural airplanes.

The silliest part is that they could have simply used a turboprop...

another reason to put the tanks there is to make for shorter pipes between the tanks and the spray nozzles. This was a pretty large aircraft for a crop duster, meant for the very large fields at Soviet collective farms, so needed a high capacity or it'd have to reload too often.

That's a Mielec M-15 Belphegor, the world's only jet powered biplane. A jet agricultural aircraft, manufactured by PZL Mielec in Poland for Soviet agricultural aviation. For its strange looks and noisy engine it was nicknamed Belphegor, after the noisy demon.
https://www.pinterest.com/pin/271764158735045150/

World's only production jet powered biplane.  Others exist

Portions of this answer appear to be plagiarized from Wikipedia.

Depending on the definition of "jet", Coandă-1910 can be counted as one. A biplane, naturally.